The invention concerns a continuously variable transmission.
A continuously variable transmission, also called a CVT, has a first cone pulley pair upon an input shaft and a second cone pulley pair upon an output shaft. Each cone pulley pair consists of one cone pulley stationary in the axial direction and one second cone pulley movable in axial direction, called the primary pulley and secondary pulley, respectively. Between the cone pulley pairs extends a belt drive organ, specifically a pushing link band The primary and secondary pulleys are adjusted by a pressure medium. For this purpose, an electronic control unit controls the pressure level of the adjustment spaces of the primary and secondary pulleys via electromagnetic actuators and hydraulic valves.
DE-OS 42 34 103 disclosed a device to control the primary pulley pressure. The device comprises an electromagnetically controlled primary valve and a hydraulic secondary valve. The primary valve is controlled by an electronic control unit. In this known device, in case of an interruption in the line from the electronic control unit to the primary valve, an emergency device is provided, wherein the pressure level of the primary pulley is determined by the secondary valve. The position of the secondary valve, in turn, is determined by the primary pulley via a mechanical coupling.
A process to control a continuously variable transmission has further been described in the Automobiltechnischen Zeitschrift ATZ, 1987, volume 89, No. 9, page 455; where both cone pulleys and the power load of two load clutches, working as a starting clutch, are adjusted via hydraulic actuation cylinders, the correct regulation of cylinder prevailing pressure being a function of: the hydraulic control unit, which ensures the belt drive organ is prestressed according to existing motor torque; and the actual ratio, in a manner resulting in a reliable power transmission without band slippage, such that the transmission ratio is adjusted, according to vehicle speed, the driver determined throttle valve position, the accelerator pedal, and the axial force upon the clutch discs is controlled making a smooth and uniform starting operation possible.
Finally, EP-B-274080 describes a continuously variable transmission system to actuate the forward input and reverse input clutches, with a line pressure source, a manual valve device optionally manually movable by the driver in order to convey fluid to the clutches in accordance with the selected driving position, a valve device to produce line control pressure according to a clutch engagement command, and an accumulator which forms a cylinder, with one piston movable therein, one first end being directly connected with the line pressure source and a connection provided with the manual valve device while one second end on the opposite side of the piston is connected with the line control pressure, and can be separated therefrom whereby the selected clutch can be supplied with fluid from the accumulator of the line pressure source.
In the continuously variable transmissions known already, not only is the primary pressure needed to adjust the primary pulley, but also a lubrication pressure must be fed to the rotating primary shaft, which is firmly connected with the primary pulley. The lubrication supply pressure and primary pressure requires adequate feed lines which must have sufficient cross sections, the primary pressure requiring a minimum cross section of about 80 mm2 and the lubrication pressure a cross section of at least about 30 mm2. This results in an accordingly large axial length and many problems are involved in keeping the minimum cross section dimensions.
The problem on which this invention is based is to provide a continuously variable transmission of reduced axial length and yet sufficient cross sections to ensure the supply of primary pressure and lubrication pressure.
Based on a transmission of the type specifically mentioned above, this problem is solved with the disclosed features.
Therefore, the invention provides that in the housing, between the primary pulley and the housing cover, there is disposed, extending substantially radially toward the center of the rotating primary shaft, a primary pressure line for the fluid required to adjust the primary pulley, which discharges in an inner cover. This ensures sealing between the cover and primary shaft. A lubrication pressure line is also provided for the rotating primary shaft.
The invention thus offers the advantage of a reduced axial length, since the primary pressure is now fed between the inner cover and the housing cover to the center of the shaft, and no longer via a hole inside the transmission cover, whose diameter must have a dimension of at least 10 mm to achieve the above indicated minimum cross section values.
According to the invention, sufficient cross sections are ensured by the fact that lubrication pressure is now conveyed within the primary pressure.